GNSS positioning using three-dimensional building models

ABSTRACT

Techniques for GNSS positioning using three-dimensional (3D) building models are described. A processor of a mobile device can determine a lower bound of uncertainty for an estimated position of the mobile device. The processor can receive an estimated position from a GNSS receiver of the mobile device. The processor can acquire geographic feature data including 3D building models of buildings and other geographic features that are located near the estimated position and may reflect GNSS signals. The processor can then determine a lower bound of uncertainty of the estimated position, regardless of an estimated uncertainty provided by a GNSS estimator. The lower bound can be higher (e.g., have a greater error margin) than the uncertainty value provided by the GNSS estimator. The processor can then present the estimated position, in association with an error margin corresponding to the lower bound of uncertainty, on a map user interface of the mobile device.

TECHNICAL FIELD

This disclosure relates generally to location determination using radiosignals.

BACKGROUND

Many modern mobile devices such as smart phones or wearable devices havenavigation functions that depend on global navigation satellite system(GNSS) signals. In challenging GNSS environment (e.g., “urban canyons”surround by signal-blocking high-rise buildings), non-line of sight(NLOS) signals and multipath interference can cause positioning errors.Using conventional technologies, a processor can identify and rejectNLOS and other distorted signals by examining signal structure. Forexample, the processor can identify and reject signals that have lowcarrier-to-noise density (C/N₀) or weak signals that are inconsistentwith strong signals. The conventional technologies typically canidentify and reject clearly distorted signals. These technologies canfail in the presence of specular reflectors, which can reflect GNSSsignals with almost no loss but can distort pseudorange and pseudorangerate measurements. In addition, if C/N₀ strength is used as a metric offidelity of a position, velocity and time (PVT) solution derived fromthe specularly reflected signals, a processor can be overconfident aboutthe PVT solution. In such situations, the horizontal uncertainty ofposition error (HEPE) or a horizontal position uncertainty in the PVTsolution can be biased incorrectly lower.

SUMMARY

Techniques for GNSS positioning using three-dimensional (3D) buildingmodels are described. A processor of a mobile device can determine alower bound of uncertainty for an estimated position of the mobiledevice. The processor can receive an estimated position from anestimator of a GNSS receiver of the mobile device. The processor canacquire geographic feature data including 3D building models ofbuildings and other geographic features that are located near theestimated position and may reflect GNSS signals. The processor can thendetermine a lower bound of uncertainty of the estimated position,regardless of an estimated uncertainty provided by a GNSS estimator. Thelower bound can be higher (e.g., have a greater error margin) than theuncertainty value provided by the GNSS estimator. The processor can thenpresent the estimated position, in association with an error margincorresponding to the lower bound of uncertainty, on a map user interfaceof the mobile device.

A processor of a mobile device can provide positioning corrections based3D building models. The mobile device can receive an estimated positionfrom a positioning source (e.g., a GNSS receiver, a Wi-Fi™ positioningcomponent, a cellular positioning component or a dead-reckoning unit) ofthe mobile device. The mobile device can acquire geographic feature dataincluding 3D building models of buildings and other geographic featuresthat are located near the estimated position and may reflect GNSSsignals. The processor can then determine a probable path for a signalfrom a GNSS space vehicle (e.g., a satellite) to reach the GNSSreceiver. The probable path can include one or more specularreflections. The processor can determine a Doppler correction based onthe probable path, including inverting a sense of a vector of theDoppler correction for each reflection. The processor can thenincorporate the Doppler correction in an estimated velocity of themobile device, an estimated position of the mobile device, or both.Alternatively or additionally, the processor can provide the Dopplercorrection to the GNSS receiver for pseudorange and pseudorange rateestimation.

The features described in this specification can achieve one or moreadvantages. For example, a mobile device implementing the techniques canreduce positioning errors in challenging GNSS environment includingurban canyons. The mobile device can reduce or avoid over-confidentlocation estimation in places where specular reflection produces nearlylossless reflections of GNSS signals in terms of C/N₀ but distorts pathsof the signals. Using the Doppler correction for specular reflections, amobile device implementing the techniques can provide position andvelocity estimates that are more accurate that available in conventionaltechnologies. The technology described in this specification can helpdistinguishing between measured Doppler uncertainty due to clock driftand Doppler uncertainty due to mis-estimation of relative motion betweenthe mobile device and a satellite. The distinction can decreasepositioning uncertainty and avoid incorrect position solutions.

The details of one or more implementations of the subject matter are setforth in the accompanying drawings and the description below. Otherfeatures, aspects and advantages of the subject matter will becomeapparent from the description, the drawings and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example mobile device handlingsignals affected by multipath interferences.

FIG. 2 is diagram illustrating example techniques of providing a lowerbound of uncertainty of an estimated position using 3D building models.

FIG. 3 is a diagram illustrating example techniques of correcting anestimated position using 3D building models.

FIG. 4 is a diagram illustrating example techniques of correctingestimated position and velocity using 3D building models.

FIG. 5A is a diagram illustrating example techniques of determiningsignal environment tiles and tile categories for positioning.

FIG. 5B is a diagram illustrating example tile categories.

FIG. 6A is a diagram illustrating example techniques of providingDoppler correction using 3D building models.

FIG. 6B is a diagram illustrating example techniques of Dopplercorrection calculation.

FIG. 7A is a block diagram illustrating components of an example systemconfigured to perform the operations of GNSS positioning using 3Dbuilding models.

FIG. 7B is a block diagram illustrating components of an examplelocation server providing geographic feature data.

FIG. 8 is a flowchart of an example process of determining a lower boundof uncertainty of an estimated position using 3D building models.

FIG. 9 is a flowchart of an example process of determining Dopplercorrection using 3D building models.

FIG. 10 is a flowchart of an example process of providing tiledgeographic feature data to a mobile device.

FIG. 11 is a block diagram illustrating an example device architectureof a mobile device implementing the features and operations described inreference to FIGS. 1-10.

FIG. 12 is a block diagram of an example network operating environmentfor the mobile devices of FIGS. 1-10.

FIG. 13 is a block diagram of a system architecture for an examplelocation server.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION GNSS Receiver Architecture

FIG. 1 is a diagram illustrating an example mobile device 102 handlingsignals affected by multipath interference. Mobile device 102 caninclude a GNSS receiver having antenna 104 and an estimator. In theexample shown, antenna 104 can detect signals from satellites 105, 106and 108 when antenna 104 is located at a particular location (e.g., onroad 110) at a particular time. The estimator can determine apseudorange and a pseudorange rate based on the signals.

At least some signals from satellites 105, 106 and 108 can reach antenna104 through one or more reflections. In the example shown, signals fromsatellites 105, 106 reach antenna 104 through signal paths 112, 114,respectively. Signal path 114 includes reflection path 115 caused by thesignal reflecting off a surface of building 118. Reflection path 115causes the signal from satellite 106 to travel a total path length thatis longer than direct LOS path 116 from satellite 106 to antenna 104.The surface of building 118 can produce a specular reflection that isnearly lossless. Accordingly, the signal traveling along reflection path115 can reach antenna 104 without significant degradation in C/No.

Mobile device 102 can use knowledge of surrounding geographic features,such as buildings 118, 122, 124, to determine possible reflection pathsand respective delays of signals on the reflection paths. In someimplementations, mobile device 102 can obtain initial location bound 120defining a geographic area that includes possible locations of antenna104. Mobile device 102 can determined initial location bound 120 basedon an estimated position, also referred to as an estimated location.

Mobile device 102 can determined the estimated position using GNSSsignals without multipath correction, using Wi-Fi™ trilateration, usingcellular information or using other location determination techniques.Initial location bound 120 can have a size (e.g., a radius if a circularbound) corresponding to an uncertainty of the estimated position.Initial location bound 120 can have any size or shape. For example,initial location bound can be circular, elliptical or square. In someimplementations, initial location bound 120 is a grid divided into anumber of grid cells. Each grid cell can correspond to a possiblelocation of antenna 104, designated as a candidate location. The gridcells can be spaced apart from one another according to a precision ofthe GNSS receiver under ideal conditions (e.g., one meter apart).

Mobile device 102 can obtain, from a local cache or a network database,a 3D building model representing features of structures that may reflectsignals reaching initial location bound 120. The features can includelocations, shapes, sizes and heights of mirror-like surfaces ofbuildings 118, 122 and 124. Mobile device 102 can obtain locations ofsatellites 105, 106 and 108 from the GNSS signals or from a networkresource or from these satellites.

Mobile device 102 can determine a lower bound of uncertainty givenmirror-like surfaces represented in the 3D building model. For example,more buildings and more mirror-like surfaces can increase the lowerbound of uncertainty. An increased lower bound of uncertainty cancorrespond to a larger error margin. The lower bound of uncertainty maybe greater than initial location bound 120. In such cases, mobile devicecan present the lower bound of uncertainty as the uncertainty areaassociated with an estimated position of mobile device 102.

In addition to determining a lower bound for error margin, mobile device102 can provide corrections to the GNSS receiver using an applicationprogramming interface (API) for the GNSS receiver. The corrections caninclude Doppler corrections for determining location and velocity ofmobile device 102. The corrections can include different covariancematrices for corresponding to different categories of terrain aspseudorange corrections. The GNSS receiver can estimate a pseudorange orpseudorange rate using the covariance matrices.

For example, mobile device 102 can provide to the GNSS receiver a listof pseudorange corrections (“δ_(Terrain)”) to be used for one or moresatellites. The GNSS receiver can then determine a range, in a PVTsolution calculation, by taking the pseudorange corrections δ_(Terrain)into calculation (1) as listed below.ρ=R+c(δ_(r)−δ^(s))+δ_(Terrain)+ϵ,  (1)where ρ is a pseudorange between antenna 104 and a satellite, R is atrue range between antenna 104 and the satellite, δ_(r) is a receiverclock error, δ^(s) is a satellite clock error, c is a speed of light,δ_(Terrain) is the pseudorange correction for a particular type ofterrain in which mobile device 102 is located, and ϵ is a randomtracking error. Mobile device 102 can then determine a position andvelocity using the corrected pseudorange.

FIG. 2 is diagram illustrating example techniques of providing a lowerbound of uncertainty of an estimated position using 3D building models.A GNSS receiver of mobile device 102 can determine estimated position202 of mobile device 102. Estimated position 202 can include latitude,longitude and optionally, altitude coordinates. Estimated position 202can be associated with estimated uncertainty 204. Estimated uncertainty204 can correspond to an error margin of estimated position 202 asdetermined by an estimator of the GNSS receiver.

Mobile device 102 can obtain a 3D building model including informationof geographic features near estimated position 202. The geographicfeatures can include location and height of buildings or otherstructures. The geographic features are near estimated position 202 ifthe geographic features can block or reflect GNSS signals from one ormore satellites to estimated position 202. In the example shown, the 3Dbuilding model includes locations and heights of buildings 206, 208, 210and 212.

Mobile device 102 can determine whether a count of the geographicfeatures that may block or reflect GNSS signals satisfies a featurecount threshold value (e.g., at least three or five). Mobile device 102can determine whether an average height of the geographic featuressatisfies a feature height threshold value (e.g., at least ten or twelvemeters). The feature count threshold value and feature height thresholdvalue can be determined empirically.

Upon determining that the feature count threshold and feature countthreshold are satisfied, mobile device 102 can determine lower bound ofuncertainty, also referred to as uncertainty floor, 214. Lower bound ofuncertainty 214 can be greater than estimated uncertainty 204,indicating that in the GNSS environment around estimated position 202,it is unlikely that the GNSS estimator can derive an error margin assmall as estimated uncertainty 204.

Mobile device 102 can determine a size and shape of lower bound ofuncertainty 214 in various ways. In some implementations, mobile device102 can determine that lower bound of uncertainty 214 is a circle havinga constant radius (e.g., 50 meters). In some implementations, mobiledevice 102 can determine that lower bound of uncertainty 214 has a sizethat corresponds to a width of an average road in the 3D building model,or a width of a road on which mobile device 102 is located, times afactor (e.g., two).

In some implementations, mobile device 102 can determine lower bound ofuncertainty 214 based on empirical statistics of GNSS performance as afunction of number and height of buildings near estimated position 202.

In some implementations, mobile device 102 can determine lower bound ofuncertainty 214 by estimating satellite visibility at estimated position202 using the 3D building model. Mobile device 102 can then estimate aquality of measurements of GNSS signals. The measurements can includepseudoranges and pseudorange rates. Mobile device 102 can computeweighted dilution of precision based on number of visible satellites.Mobile device 102 can determine a line of sight (LOS) vector Ui for agiven satellite SVi using equation (2) below.U _(i)=[cos(El _(i))*sin(Az _(i)),cos(El _(i))*cos(Az _(i)),sin(El_(i))],  (2)where U_(i) is an LOS unit vector for satellite SV_(i), directed fromthe user's location to SVi, Az_(i) is the azimuth for satellite SV_(i),and El_(i) is the elevation for satellite SV_(i). Mobile device 102 canthen determine a geometry matrix as follows, using the LOS vectors forthe visible satellites and using equation (3) below.

$\begin{matrix}{{G = \begin{bmatrix}{{- U_{1}},1} \\{{- U_{2}},1} \\\ldots \\{{- U_{n}},1}\end{bmatrix}},} & (3)\end{matrix}$where G is the geometry matrix and U_(i) is an LOS vector for satelliteSV_(i).

Mobile device 102 can determine a dilution of precision (DOP) matrix Has follows, using the geometry matrix G as determined above and usingequation (4) below.H=inv(G′*G),  (4)where G′ is the transpose of geometry matrix G.

Mobile device 102 can determine a horizontal dilution of precision(HDOP) as follows, using the DOP matrix Has determined above and usingequation (5) below.HDOP=√{square root over (H(1,1)+H(2,2))}  (5)

Mobile device 102 can then determine lower bound of uncertainty 214using the horizontal dilution of precision HDOP and equation (6) below.unc_floor=HDOP*σ_(URE),  (6)where unc_floor is lower bound of uncertainty 214 and σ_(URE) is a userrange error.

In some implementations, mobile device 102 can determine a weight matrixW based on probability of satellite visibility based on the 3D buildingmodel. In addition, mobile device 102 can determine the weight matrix Wusing other factors, e.g., C/N₀ of each of the signals. In suchimplementations, equation (4) above can be modifies as follows, as shownin equation (7) below.H=inv(G′*W*G),  (7)where G is the geometry matrix and W is the weight matrix.

Mobile device 102 can then present estimated position 202 and a newerror margin corresponding to lower bound of uncertainty 214. In caselower bound of uncertainty 214 is smaller than estimated uncertainty204, mobile device 102 can present estimated uncertainty 204 instead.Lower bound of uncertainty 214 can have any geometric shape. Forexample, lower bound of uncertainty 214 can be a circle, ellipse orpolygon.

FIG. 3 is a diagram illustrating example techniques of correcting anestimated position using 3D building models. Mobile device 102 islocated outside of building 210. A GNSS receiver of mobile device 102can determine estimated position 302 of mobile device 102. Due tomultipath interferences caused by specular reflections of GNSS signals,the GNSS receiver incorrectly determines latitude and longitudecoordinates of mobile device 102, which are located inside of building210. Estimated position 302 has estimated uncertainty 304. Due to nearlylossless reflections in the signal paths, the GNSS receiver assigns alow uncertainty value to the estimated position 302. Accordingly,estimated uncertainty 304 is small and entirely contained in thefootprint of building 210, which is incorrect.

Using techniques described in reference to FIG. 2, mobile device 102 candetermine lower bound of uncertainty 306. In some implementations,mobile device 102 can associate lower bound of uncertainty 306 withestimated position 302, and determine if area defined by lower bound ofuncertainty 306 extends beyond building 210. If yes, mobile device 102can present lower bound of uncertainty 306 in association with estimatedposition 302 on a map user interface. If no, mobile device 102 canenlarge lower bound of uncertainty 306 until the area defined by lowerbound of uncertainty 306 extends beyond building 210. Mobile device 102can then present enlarged lower bound of uncertainty 306 in associationwith estimated position 302 on a map user interface.

In some implementations, mobile device 102 can adjust estimated position302 based on the 3D building model. The adjustment can include movingestimated position 302 to new location 308 that is outside of building210. Moving estimated position 302 to new location 308 can beconditioned upon a velocity of mobile device 102. For example, mobiledevice 102 can move estimated position 302 upon determining that amagnitude of the velocity of mobile device 102 exceeds a speedthreshold, indicating, for example, mobile device 102 is in a movingvehicle.

FIG. 4 is a diagram illustrating example techniques of correctingestimated position and velocity using 3D building models. A GNSSreceiver of mobile device 102 can determine that mobile device 102 at avelocity that has a magnitude and a direction. Mobile device 102 candetermine, based on the magnitude, that likelihood that mobile device iscarried by a pedestrian is lower than a threshold value. Accordingly,mobile device 102 can determine that mobile device 102 is unlikely toenter a building. Based on the direction, mobile device 102 candetermine mobile device 102 moves along path defined by locations 402A,402B, 402C, 402D, 402E and 402F. Each of locations 402A through 402F isan estimated position of mobile device 102 at a particular time. In FIG.4, each of locations 402A through 402F is associated with an arrowhaving a length corresponding to a magnitude of the velocity at acorresponding estimated position. Each arrow has a directioncorresponding to a direction of movement of mobile device 102 at eachrespective estimated position.

Mobile device 102 can determine, using a 3D building model, thatbuildings 410 and 412 are located within a threshold distance of mobiledevice 102 to interfere with GNSS signal reception. In addition, mobiledevice 102 can determine that the path of mobile device 102 intersectsbuilding 410. Accordingly, mobile device 102 can modify the path.Modifying the path can include moving estimated positions 402C and 402Dto new locations 414 and 416. Mobile device 102 can determine locations414 and 416 out of building 410 using various factors. For example,mobile device 102 can select locations 414 and 416 that minimally impactthe validity of magnitudes and directions of the velocity of mobiledevice 102 measured earlier. Mobile device can associate new velocities418 and 420 to mobile device 102. The new velocity may have directionadjusted based on shape of building 410 as defined in the 3D buildingmodel. Mobile device 102 can then present a new path for display. Thenew path can be defined by locations 402A, 402B, 414, 416, 402E and402F.

FIG. 5A is a diagram illustrating example techniques of determiningsignal environment tiles and categories for positioning. Mobile device102 can fetch geographic feature data including 3D building models on anas-needed basis from location server 502. Location server 502 caninclude one or more computers configured to receive request from, andprovide data to, mobile device 102 through a communications network(e.g., the Internet).

Location server 502 can include signal environment tile database 504.Signal environment tile database can store geographic feature dataincluding information on geographic features in geographic area 506(e.g., the world). Location server 502 can organize the information assignal environment tiles. Each signal environment tile can correspond toa patch of geographic region defined by latitude and longitudecoordinates.

For example, location server 502 can represent a portion 508 ofgeographic area 506 as signal environment tiles 512, 514, 516, 518, 520,522, 524, 526 and 528. Each of the tiles can be an M-by-N degree (e.g.,0.05 degrees latitude by 0.05 degrees longitude) geometric shapeapproximating a rectangle (not drawn to scale). Each geometric shape cancover a respective geographic region.

Each of the tiles can be associated with a tile category corresponding atype of signal reflection that may affect GNSS reception. For example,signal environment tiles 518 and 524 can be associated with a first tilecategory (e.g., “open water”) indicating that reflection of GNSS signalswill most likely be caused by bodies of water in the correspondingregions. Signal environment tiles 512 and 514 can be associated with asecond category (e.g., “rural”) indicating that reflection of GNSSsignals will most likely be caused by ground and isolated buildings inthe corresponding regions. Signal environment tile 516 can be associatedwith a third category (e.g., “simple urban”) indicating that reflectionof GNSS signals will most likely be caused by sparsely distributedbuildings in the corresponding region. Signal environment tiles 520, 522and 528 can be associated with a fourth category (e.g., “dense urban”)indicating that reflection of GNSS signals will most likely be caused byconnected or densely distributed buildings in the corresponding regions.Signal environment tile 528 can be associated with a fifth category(e.g., “urban canyon”) indicating that reflection of GNSS signals willmost likely be caused by multiple tall buildings having mirror-likesurfaces in the corresponding region.

Each signal environment tile may include one or more 3D building modelsthat include information on geographic features located in the tile. Forexample, signal environment tile 528 may include locations, footprints,and heights of buildings, billboards, bridges and other structures in acorresponding geographic region.

Mobile device 102, upon determining an initial estimated position, cansubmit that estimated position to location server 502. In response,location server 502 can provide to mobile device 102 one or more signalenvironment tiles that cover that estimated position or are closest tothat estimated position. Each signal environment tile can be associatedwith a tile category. Mobile device 102 can determine, based on the tilecategory, whether to proceed to download the 3D building models in thesignal environment tile.

For example, mobile device 102 can submit an estimated position andreceives signal environment tile 528 enclosing the estimated position.Signal environment tile 528 has a particular tile category (e.g., “urbancanyon”) that has a value indicating that 3D building models can improvepositioning performance. Based on the indication, mobile device 102 cansubmit a request to location server 502. Location server 502 thenprovides 3D building model 530 for download. 3D building model 530 caninclude information on structures 532, 534 and 536 that are located inproximity to the estimated position. Mobile device 102 can thendetermine which of structures 532, 534 or 536 may block or reflect asignal from a GNSS satellite given a position of the GNSS satellite andan estimated position of mobile device 102. The knowledge on whichsatellite signal is blocked or reflect can help determine a lower boundof uncertainty in position estimation.

In addition, mobile device 102 can provide the variance corresponding tothe particular signal environment tile to a GNSS receiver for locationestimation and correction. Mobile device 102 can provide the variancethrough an application programming interface (API). For example, the APImay specify that the GNSS receiver can receive the variances from mobiledevice 102, or that the GNSS receiver can receive an enumerated type(enum) data item (e.g., 0, 1, 2, 3 . . . ) where each value in the dataitem corresponds to a respective category (e.g., 0 for “open water” and4 for “urban canyon”). Using the enum data item, the GNSS receiver canperform a lookup in a firmware storage device to determine pre-loadedvariances. The GNSS can pre-load or change the variances during afirmware update.

FIG. 5B is a diagram illustrating example tile categories. Each signalenvironment tile may be associated with a respective relationshipbetween pseudorange variance and satellite position that is specific tothe category of that tile. The variance can correspond to empiricallydetermined location error margin in the region corresponding to thattile. The tile category of a signal environment tile can indicate thatrelationship.

For example, signal environment tile 512 (of FIG. 5A) can correspond toa tile category “rural” indicating relationship 542. As shown in FIG.5B, in a signal environment for “rural” tile category, pseudorangeuncertainty (as measured by variance σ_(Range) ²) decreases as satelliteelevation (as measured by degrees from horizon) increases. The rate ofdecrease is at a first level.

A tile category that corresponds to more reflecting and blockingfeatures can be associated with a higher uncertainty. For example,signal environment tile 528 (of FIG. 5A) can correspond to a tilecategory “urban canyon” indicating relationship 548. As shown in FIG.5B, in a signal environment for “urban canyon” tile category,pseudorange uncertainty (as measured by variance σ_(Range) ²) decreasesas satellite elevation (as measured by degrees from horizon) increases.The rate of decrease is at a second level that is slower than the firstlevel. In addition, at same satellite elevation 550, the uncertaintyassociated with signal environment tile 528 is higher. Accordingly,location server 502 or mobile device 102 can determine that if anestimated position corresponds to signal environment tile 512 havingtile category “rural” (or another representative value), additionaldownload of 3D building models is unnecessary. In contrast, locationserver 502 or mobile device 102 can determine that if an estimatedposition corresponds to signal environment tile 528 having tile category“urban canyon” (or another representative value), additional download of3D building models is beneficial.

FIG. 6A is a diagram illustrating example techniques of providingDoppler correction using 3D building models. Mobile device 102 canestimate and correct effects of multipath interferences on measuredpseudoranges and pseudorange rates using 3D building models coupled withestimated position and estimated velocity. Estimating expected Dopplershift on a GNSS signal based on the estimated position and velocity andbased on surrounding building geometry can aid acquisition and improvetime to first fix (TTFF) and power cost.

At a given time, mobile device 102 may be located at estimated position602 having estimated uncertainty 604. Mobile device 102 may have anestimated velocity 606. Estimated velocity 606 has a direction thatpoints away from satellite 608 of a GNSS system. Structure 616, locatedbetween mobile device 102 and satellite 608, blocks direct LOS signalpath 612 between estimated position 602 and satellite 608. Sincedirection of velocity 606 points away from satellite 608, the truerelative velocity is difference between a projection of satellitevelocity 614 and a projection of velocity 606 along vector of LOS signalpath 612.

In the example shown, mobile device 102 receives reflected signal from amirror-like surface of structure 616. Accordingly, the measured Dopplerdrift is erroneous. In particular, measured relative velocity isincreased by velocity 606 along a reflection vector of segment 618 of asignal path. Likewise, measured pseudo-range suffers in the direction ofthe reflection vector.

Mobile device 102 can estimate the errors caused by structures 610 and616 based on estimated velocity 606, satellite velocity 614, andgeometry of structures 610 and 616 surrounding mobile device 102.Estimating of pseudorange error can be based at least in part onestimated position 602. The measured Doppler effect can be based atleast in part on estimated velocity 606. In pure NLOS scenarios as shownin FIG. 6A, error caused by the sense of relative motion betweensatellite 608 and mobile device 102 can double. Accordingly, mobiledevice 102 can inverse relative sense of motion of mobile device 102 andmotion of satellite 608. The inversion can provide correction tomeasured pseudorange rate. Mobile device 102 can then couple thecorrection in a velocity estimate to position estimate via a systemmodel in a statistical filter (e.g., a Kalman filter).

Mobile device 102 can create a sampling grid around estimated position602 and designate multiple candidate locations based on position errordistribution. The position error distribution can be based on estimateduncertainty 604, or based on a lower bound of uncertainty in positionestimation as determined using a 3D building model representingstructures 610 and 616.

Mobile device 102 can determine, based on constellation of GNSSsatellites and a 3D building model, which satellites are partially orentirely blocked. Mobile device can determine correspondinguncertainties for each respective satellite that is blocked. Mobiledevice 102 can determine a probable path signal for signals from avisible satellite to mobile device 102. In the example shown, theprobably signal path include segments 618 and 620.

Mobile device 102 can computed estimated Doppler corrections anduncertainty from the probable signal path. Mobile device 102 candetermine the Doppler correction based on component of velocity 606projected on a probably LOS vector. In the example shown, the projectedLOS vector is a vector of path segment 620. Mobile device 102 candetermine reflections on the probable path, e.g., specular reflection622. Mobile device 102 can inverse a sense for the Doppler correctionfor each reflection. Accordingly, after the correction, mobile device102 can determine a pseudorange rate based on knowledge that, althoughDoppler shift as measured by a GNSS receiver indicates that mobiledevice 102 is moving towards satellite 608, the reflection results inthe Doppler shift indicates that mobile device 102 is moving away fromsatellite 608.

Mobile device 102 can compute estimated pseudorange correction andassociated uncertainty based on the Doppler correction. Mobile device102 can augment innovations of a Kalman filter and associateduncertainties using the Doppler corrections, reorder innovations basedon updated uncertainties for a Chi-square test, and check and processcorrected innovations. Checking and processing corrected innovations caninclude discarding and preserving pseudoranges and pseudorange ratesafter taking into consideration Doppler shifts caused by thereflections. In some implementations, mobile device 102 can provide theDoppler correction to a GNSS receiver through an API specifyingformation and parameters for communication. The GNSS receiver can beprogrammed to perform some or all of the tasks, including computingpseudorange corrections and subsequent tasks.

By taking into account effects on Doppler shift caused by specularreflection 622, mobile device 102 can distinguish measured Dopplereffect uncertainty caused by clock drift and measured Doppleruncertainty caused by mis-estimation of relative motion between mobiledevice 102 and satellite 608. The distinction maybe otherwiseundetectable. By distinguishing measured Doppler effect caused by clockdrift and effect caused by specular reflection 622, mobile device 102can improve performance in position estimation. For example, in aChi-square test, mobile device 102 may preserve residuals of a Kalmanfilter that would otherwise be rejected for being low quality, upondetermining that the fault in the residuals are caused by reflection 622rather than by other random factors, and upon correcting the Dopplershift accordingly. Fewer rejections can result in reduced positioninguncertainty. Fewer rejections can also lead to greater tolerance toclock drift.

FIG. 6B is a diagram illustrating example techniques of Dopplercorrection calculation. Mobile device 102 can travel at a user velocityū. User velocity ū can be a vector having components 642A, 642B and 642Cin a geographic coordinate system, e.g., an east, north, up (ENU)coordinate system. Mobile device 102 can move toward reflective surface644, e.g., a reflective surface of structure 616.

Satellite 608 providing a GNSS signal may move at satellite velocity v_(s) in the geographic coordinate system. Satellite velocity v _(s) canhave components 646A, 646B and 646C in the geographic coordinate system.Due to reflection from reflective surface 644, as measured by mobiledevice 102, satellite 608 may appear at location 648, which has anapparent elevation of a Satellite 608 can have measured satellitevelocity v _(s), having components 650A, 650B and 650C in the geographiccoordinate system.

Mobile device 102 can determine the Doppler correction usingcalculations as described below. Mobile device 102 can Doppler shift asfollows, using equation (8).

$\begin{matrix}{{\frac{\Delta\; f}{f} = \frac{v_{R}}{c}},} & (8)\end{matrix}$where Δf is the Doppler shift, f is the baseline frequency for the GNSSsignal (e.g., 1575.42 MHz), v_(R) is a relative velocity betweensatellite 608 and mobile device 102, and c is the speed of light.

Mobile device 102 can determine components of user velocity ū andmeasured satellite velocity v _(sR) as follows, using equations (9) and(10), respectively.ū _(R)=(ū·n _(uR)) n _(sR),  (9)where ū_(R) is the component of the user velocity u on reflected signalpath 652, n _(uR) is a unit vector along reflected signal path 652.v _(sR)=( v _(s′) ·n _(sR)) n _(sR),  (10)where v _(S′) is the reflected velocity of satellite 608 with respect toreflective surface 644, v _(sR) is the component of v _(s), along thereflected path from SV to user, n _(sR) is a unit vector along reflectedsignal path 652.

Mobile device 102 can determine that measured satellite velocity v _(s′)can change senses for each reflection, as described in equation (11)below.v _(s′) =v _(s)−2( v _(s) ·n _(B)) n _(B),  (11)where v _(s) is the satellite velocity, n _(B) is unit normal vectorperpendicular to reflective surface 644.

Accordingly, a component of velocity perpendicular to reflective surface644 is inverted due to the reflections. Accordingly, mobile device 102can determine the v_(R) of equation (8) as follows, using equation (12).

$\begin{matrix}\begin{matrix}{v_{R} = {{{\overset{\_}{v}}_{s^{\prime}} \cdot {\overset{\_}{n}}_{sR}} - {\overset{\_}{u} \cdot {\overset{\_}{n}}_{uR}}}} \\{= {{\left\lbrack {{\overset{\_}{v}}_{s} - {2\left( {{\overset{\_}{v}}_{s} \cdot {\overset{\_}{n}}_{B}} \right){\overset{\_}{n}}_{B}}} \right\rbrack \cdot {\overset{\_}{n}}_{sR}} - {\overset{\_}{u} \cdot {\overset{\_}{n}}_{uR}}}}\end{matrix} & (12)\end{matrix}$

Accordingly, mobile device 102 can determine that measured Doppler shiftsatisfies the following.

$\begin{matrix}\begin{matrix}{{\Delta\; f_{measured}} = {\frac{v_{R}}{c}f}} \\{{= {\frac{f}{c}\left\{ {{\left\lbrack {{\overset{\_}{v}}_{s} - {2\left( {{\overset{\_}{v}}_{s} \cdot {\overset{\_}{n}}_{B}} \right){\overset{\_}{n}}_{B}}} \right\rbrack \cdot {\overset{\_}{n}}_{sR}} - {\overset{\_}{u} \cdot {\overset{\_}{n}}_{uR}}} \right\}}},}\end{matrix} & (13)\end{matrix}$where Δf_(measured) is measured Doppler shift. Accordingly, mobiledevice 102 can determine the Doppler correction based on the relativevelocity of satellite 608 and mobile device 102 along reflected path652.

The number of reflections is a factor, and may not be the soledeterminant in the correction. For example, with an odd number ofreflections, the Doppler shift is the opposite of the direct LOS Dopplershift, whereas and even number of reflections can make the sense of theshift the same as the LOS case. Mobile device 102 can determine thecorrection based on relative difference between the user velocitycomponent along reflected signal path 652 and the satellite velocitycomponent along the reflected path.

In contrast, expected Doppler shift in the absence of reflections can beexpressed below in equation (14).

$\begin{matrix}{{{\Delta\; f_{expected}} = {\frac{f}{c}{\left( {{\overset{\_}{v}}_{s} - \overset{\_}{u}} \right) \cdot n_{uS}}}},} & (14)\end{matrix}$where Δf_(expected) is the expected Doppler shift in the absence ofreflections, n_(uS) is a unit vector on direct LOS 612. Mobile device102 can determine a Doppler correction according to a difference betweenthe expected Doppler shift in the absence of reflections and themeasured Doppler shift, using equation (15) below.

$\begin{matrix}{{k = {\frac{f}{c}\left\lbrack {{\left( {{\overset{\_}{v}}_{s} - \overset{\_}{u}} \right) \cdot n_{uS}} - \left( {{{\overset{\_}{v}}_{s^{\prime}} \cdot {\overset{\_}{n}}_{sR}} + {\left( {- 1} \right)^{n}{\overset{\_}{u} \cdot {\overset{\_}{n}}_{uR}}}} \right)} \right\rbrack}},} & (15)\end{matrix}$where k is the Doppler correction. For clarity, the correction isdescribed in reference to a generic satellite, satellite 608. For a GNSSconstellation having multiple satellites, mobile device 102 candetermine a respective Doppler correction for each of the satellites.

FIG. 7A is a block diagram illustrating components of example system 700configured to perform the operations of GNSS positioning using 3Dbuilding models. System 700 can be implemented on a mobile device, e.g.,mobile device 102. System 700 can include one or more computerprocessors programmed to perform operations of location determinationusing 3D building models.

System 700 can include, or be coupled to, GNSS receiver 702. GNSSreceiver 702 can include an antenna and a global positioning system(GPS) processor configured to determine one or more estimated PVT valuesfrom satellite signals. Each of the estimated position, velocity andtime may be associated with a respective uncertainty value. GNSSreceiver 702 can provide the estimated PVT, as well as the associateduncertainty values, to server interface 704.

Server interface 704 is a component of system 700 configured to receiveestimated PVT from GNSS receiver 702 and request one or more tiles of 3Dbuilding models. Server interface 704 can submit the request to locationserver 502 as described above in reference to FIG. 5. The request caninclude the estimated position, velocity, time or any combination of theabove.

Upon receiving the one or more tiles of 3D building models from locationserver 502, system 700 can store the received tiles in local buildingmodel cache 706. System 700 can update local building model cache 706upon entering or predicted to be entering a new geographic region.

System 700 can include feature analyzer 708. Feature analyzer 708 is acomponent of system 700 configured to determine number of geographicfeatures that may affect GNSS signal reflection, heights of thesegeographic features, geometry of these features, location and geometryof mirror-like surfaces, number of satellites visible by GNSS receiver702, and other factors that geographic features may affect locationdetermination. Feature analyzer 708 can make the determination using thetiles stored in local building model cache 706 and the PVT values andassociated uncertainties provided by GNSS receiver 702.

System 700 can include uncertainty lower bound module 710. Uncertaintylower bound module 710 is a component of system 700 configured todetermine a lower bound of uncertainty based on output from featureanalyzer 708. Uncertainty lower bound module 710 can determine the lowerbound in various ways, including, for example, based on a feature countthreshold value and a feature height threshold value or based on anumber of visible satellites and a weight matrix. Uncertainty lowerbound module 710 can provide the lower bound of uncertainty to locationpresentation module 712.

Location presentation module 712 is a component of system 700 configuredto present an estimated position and associated uncertainty on a userinterface. The user interface can be a virtual map displayed on mobiledevice 102, audio or visual turn-by-turn navigation instructions, or anycombination of the above. In some implementations, Location presentationmodule 712 can provide the estimated position and associated uncertaintyto a computer program (e.g., a program that provides location-basedservices) as inputs. Location presentation module 712 can obtain theestimated position from GNSS receiver 702. Location presentation module712 can designate the lower bound of uncertainty received fromuncertainty lower bound module 710 as the uncertainty associated withthe estimated position.

System 700 can include Doppler correction module 714. Doppler correctionmodule 714 is a component of system 700 configured to receive outputincluding counts, locations, shapes and sizes of mirror-like surfacesaround an estimated position. Doppler correction module 714 can thendetermine the Doppler corrections based on the output, as describedabove in reference to FIGS. 6A and 6B. Doppler correction module 714 canprovide the Doppler corrections to GNSS receiver 702 for furtherprocessing, e.g., for correcting pseudorange and pseudorange ratecalculations.

System 700 can include Doppler correction module 714. Doppler correctionmodule 714 is a component of system 700 configured to receive outputincluding counts, locations, shapes and sizes of mirror-like surfacesaround an estimated position. Doppler correction module 714 can thendetermine the Doppler corrections based on the output, as describedabove in reference to FIGS. 6A and 6B. Doppler correction module 714 canprovide the Doppler corrections to GNSS receiver 702 for furtherprocessing, e.g., for correcting pseudorange and pseudorange ratecalculations.

System 700 can include terrain correction module 716. Terrain correctionmodule 716 is a component of system 700 configured to determine variousparameters to correct based on output of feature analyzer 708. Forexample, variance of a pseudorange (σ_(Range) ²) can be a function forsatellite elevation, where a higher satellite elevation correspond to alower variance. The rate of decrease of variance corresponding toincrease in elevation can be different for different terrains. Eachparticular terrain category can correspond to a different curve for thedecrease. Terrain correction module 716 can determine a respectivefunction for each terrain category, and provide a specific function toGNSS receiver for determining the uncertainty of pseudoranges,pseudorange rates, or uncertainty in a PVT solution.

GNSS receiver 702 can include device interface 718. Device interface 718is a component of GNSS receiver 702 configured to receive input fromDoppler correction module 714 and terrain correction module 716according an API specifying parameters and formats. For example, the APIcan include a specification indicating that GNSS receiver 702 canreceive an enumerated type value, where each value can indicate aparticular relationship between pseudorange uncertainty and satelliteelevation. Upon receiving a value, GNSS receiver 702 can use thecorresponding relationship in estimating pseudorange uncertainty.

System 700 can include location correction module 720. Locationcorrection module 720 is a component of system 700 configured to receiveestimated PVT values, associated uncertainty from GNSS receiver 702, andreceive output from feature analyzer 708 Location correction module 720can then determine position, velocity, and uncertainty corrections onoutput from GNSS receiver 702 based on geographic features. Thecorrection can include moving the estimated position, changing adirection of the velocity, and increasing or decreasing the uncertainty.Location correction module 720 can provide corrected PVT values anduncertainty to location presentation module 712.

FIG. 7B is a block diagram illustrating components of example locationserver 502 providing geographic data. Location server 502 can includeone or more processors programmed to perform various operations.

Location server 502 can include geographic data interface 742.Geographic data interface 742 is a component of location server 502configured to receive geographic data from various sources. The data caninclude Wi-Fi™ access point data, survey data, satellite images, 3Dbuilding models etc. In some implementation, geographic data interface742 can determine the 3D building models from data supplied by variouscomputer systems in various formats.

Geographic data interface 742 can provide the geographic data to tilemodule 744. Tile module 744 is a component of location server 502configured to group the geographic data to signal environment tilesbased on location. Each tile can include a geometric shape (e.g., arectangle) that encloses a set of features. Tile module 744 can providethe signal environment tiles to tile category module 746.

Tile category module 746 is a component of location server 502configured to compare information on geographic features in each signalenvironment tile with category data to determine a tile category foreach signal environment tile. The category data can include empiricaldata derived from surveys on how geographic features of various terrainsof each tile category affect GNSS signal reception. The category datacan include data derived from models of signal propagation in thevarious terrains of each tile category. Location server 502 can storecategory data in category database 747.

Tile category module 746 can associate a tile category that matches bestwith geographic data of a signal environment tile with that tile. Tilecategory module 746 can store the signal environment tiles andassociated tile categories in signal environment tile database 504.Location server 502 can include device interface 748. Device interface748 is a component of location server 502 configured to receive arequest from a mobile device, e.g., mobile device 102. The request caninclude an estimated position. Device interface 748 can provide a tiletype associated of a tile enclosing the estimated position as a responseto the request. If the estimated position is associated with anuncertainty, the estimated position can have an error margin andassociated with an area that may span multiple signal environment tiles.Device interface 748 can provide tile types of all signal environmenttiles intersecting the estimated position as a response.

The request can include an indicator indicating that 3D building modelsare requested for an estimated position. In response, device interface748 can determine 3D building models of geographic features thatsurround the estimated position to the mobile device. Geographicfeatures that surround the estimated position can be features that arein one or more signal environment tiles that enclose the estimatedlocation.

Exemplary Procedures

FIG. 8 is a flowchart of example process 800 of determining a lowerbound of uncertainty of an estimated position using 3D building models.Process 800 can be executed by a processor, e.g., a computer processorof mobile device 102.

The processor can receive (802) from a GNSS receiver an estimatedposition of the mobile device. The estimated position can includeestimated geographic coordinates of latitude, longitude and altitude.The estimated position can be associated with an uncertainty value thatcorresponds to an error margin (e.g., in meters).

The processor can receive (804) geographic feature data, e.g., 3Dbuilding models. The geographic feature data can include locations,shapes and heights of geographic features that are located sufficientlyclose to the estimated position to interfere with signals received bythe GNSS receiver. A 3D building model can include a model of anygeographic feature that may interfere with signal reception, includingnatural and man-mad geographic features other than buildings.

Receiving the geographic feature data can include performing thefollowing operations. The processor or a location server (e.g., locationserver 502 of FIG. 5) can determine a signal environment tile based onthe estimated position. The signal environment tile can correspond to ageographic region. The geographic region being an area surrounding theestimated position of the mobile device. The signal environment tile canrepresent geographic features located in that geographic region that mayinterfere with GNSS signal reception. Based on a tile category of thesignal environment tile, the processor or location server can determinethat the geographic feature data of the signal environment tile canimprove position estimate. The processor or the location server cansubmit to a signal environment tile database (e.g., signal environmenttile database 504) the estimated position of the mobile device or anidentifier of the signal environment tile. The signal environment tiledatabase can store 3D models on geographic features including the 3Dbuilding model 530 of FIG. 5. The 3D models can be organized as signalenvironment tiles. The processor can receive the geographic feature datacorresponding to the signal environment tile from the signal environmenttile database.

The processor can determine (806) a lower bound of uncertainty of theestimated position that is achievable by the GNSS receiver when the GNSSreceiver is located among the geographic features. The processor canmake the determination based on at least one of the locations of thegeographic features, a count of the geographic features, or the heightsof the geographic features.

The processor can determine the lower bound when certain conditions aremet. In some implementations, determining the lower bound of uncertaintycan include determining whether the count of the geographic featureslocated sufficiently close to the GNSS receiver to interfere receptionof the GNSS signals satisfies a feature count threshold. The processorcan determine whether an average of heights of the geographic featureslocated sufficiently close to the GNSS receiver to interfere receptionof the GNSS signals satisfies a feature height threshold. The processorcan then determine the lower bound of uncertainty when both the featurecount threshold and feature height are satisfied.

The processor can determine a value of the lower bound of uncertainty invarious ways. In some implementations, determining the lower bound ofuncertainty can be based on a predetermined factor and a width of anaverage road located in the geographic region enclosing the estimatedposition of the mobile device. For example, the lower bound can be twotimes the average road width in the region.

In some implementations, determining the lower bound of uncertainty caninclude determining satellites that visible by the GNSS receiver at theestimated position. The processor can determine a weight dilution ofprecision based on the visible satellites. The processor can thendetermine the lower bound of uncertainty based on the weight dilution ofprecision.

The processor can designate (808) a representation of the lower bound ofuncertainty as a new uncertainty value of the estimated position. Forexample, the processor can increase the uncertainty value upondetermining that the uncertainty value has smaller error margin than thelower bound of uncertainty. The processor can display a representationof the estimated position on a map displayed on a surface of the mobiledevice, for example, as a circle or marker. A size of the circle ormarker can represent the lower bound of uncertainty.

In some implementations, the processor can determine a pseudorangetracking error matrix including elements indicating uncertainty valueson various dimensions of pseudorange estimation. The processor canprovide the pseudorange tracking error matrix as the pseudorangecorrection δ_(Terrain) to the GNSS receiver for estimating the positionof the mobile device.

In some implementations, the processor can determine that the estimatedgeographic coordinates in the estimated position of the mobile deviceindicate a position inside of a geographic feature. In response, theprocessor can designate a set of geographic coordinates outside of thegeographic feature as new estimated geographic coordinates of theestimated position, as described above in reference to FIGS. 3 and 4.

FIG. 9 is a flowchart of an example process of determining Dopplercorrection using 3D building models. Process 900 can be executed by aprocessor, e.g., a computer processor of mobile device 102.

The processor can determine (902) multiple candidate locations of themobile device based on an estimated position provided by a GNSS receivercoupled to the mobile device. Determining the candidate locations caninclude determining a sampling grid around the estimated position and inan area defined by an uncertainty value associated with the estimatedposition. The processor can designate locations on the sampling grid asthe candidate locations.

The processor can receive (904) geographic feature data. The geographicfeature data, e.g., 3D building models, can include locations andheights of geographic features that are estimated to interfere withsignals received by the GNSS receiver.

The processor can determine (906) an estimated signal path for a signalto reach from a satellite of the GNSS to the GNSS receiver. Determiningthe estimated signal path can include determining one or morereflections of the signal by the geographic features and determining anuncertainty value for the signal path based on the candidate locations.Determining the estimated signal path can include determining aprobability value associated with the signal path based on the candidatelocations. For example, in some implementations more candidate locationsat which the GNSS receiver can receive the signal along the estimatedsignal path can correspond to a higher probability value for the path.

The processor can estimate (908) a Doppler correction of the signalbased on a count of the reflections in the signal path. For eachreflection, the processor can invert a sense of a vector of the Dopplercorrection. Estimating the Doppler correction can include estimating acomponent of user velocity projected along a segment of the estimatedsignal path. The segment can be the last segment of the signal pathbetween a last reflection point and the GNSS receiver. In estimating theDoppler correction, the processor can estimate an uncertainty valueassociated with the Doppler correction based on various factors. Forexample, a higher C/N₀ value of a received signal can correspond to alower uncertainty value.

The processor can provide (910) the estimated Doppler correction to theGNSS receiver for estimating at least one of a position of the mobiledevice or a velocity of the mobile device. In some implementations, theprocessor or the GNSS receiver can estimate a carrier Doppler shiftbetween the satellite and the mobile device. The processor or the GNSSreceiver can augment Kalman filter innovations and associateduncertainties using the Doppler correction. The processor or the GNSSreceiver can order the Kalman filter innovations based on updateduncertainties. The processor or the GNSS receiver can feed the orderinnovations as input for a Chi-square test.

The processor or the GNSS receiver can perform the Chi-square test onthe ordered innovations to reject those pseudorange or pseudorangerates. Accordingly, reflections and uncertainty of reflections, inaddition to the conventional C/N₀ values and satellite elevations, canbe bases for determining signal reliability by the Chi-square test. Theadditional bases can result in position and velocity estimation usingmore reliable pseudorange or pseudorange rate measurements. In someimplementations, the processor can determine a receiver clock errorbased on the Doppler correction.

FIG. 10 is a flowchart of example process 1000 of providing tiledgeographic data to a mobile device. Process 1000 can be executed by asystem including one or more processors. The system can include, forexample, location server 502 of FIG. 5

The system can receive (1002) geographic information on geographicfeatures in a geographic area. The geographic features can includestructures that are estimated to interfere with reception of wirelesssignals at a location in the geographic area. The geographic informationcan be provided by one or more information sources, and include, forexample, a wireless access point density in various regions of thegeographic area, a digital surface model of the geographic area, a 3Dbuilding model of the geographic area, a geographic survey of thegeographic area, a satellite image of the geographic area, or anycombination of the above.

The system can group (1004) the geographic information into signalenvironment tiles of geographic feature data. Each signal environmenttile can include a geometric shape occupying a respective geographicregion in the geographic area. Each geometric shape can be a polygonrepresented by latitude and longitude coordinates, or athree-dimensional block represented by latitude, longitude and altitudecoordinates.

The system can assign (1006) a respective tile category to each signalenvironment tile. Each tile category can correspond to a specified rangeof density and heights of geographic features. Each tile category canindicate a respective relationship between an uncertainty in GNSSpositioning and a position of a satellite of the GNSS as viewed from aGNSS receiver located in the geographic region of the tile. Therelationship can be affected and constrained by geographic featureslocated in the corresponding geographic region.

For example, a first signal environment tile can have a first tilecategory (e.g., “rural”). A second geographic environment tile has asecond category (e.g., “urban canyon”). The first tile category and thesecond tile category can indicate that density and heights of geographicfeatures in a geographic region of the first signal environment tile areless than density and heights of geographic features in geographicregion the second signal environment tile. The system can assign a loweruncertainty pseudorange or pseudorange rate uncertainty to the firsttile than to the second tile, given a same satellite elevation.

Upon receiving a request that indicates an estimated position from amobile device, the system can provide (1008) a tile category assigned toa signal environment tile of a geometric region enclosing the estimatedposition as a response to the request. One or more values (e.g., “denseurban,” “urban canyon” or both) of a tile category can trigger themobile device to perform various operations. These operations caninclude, for example, enabling an inertial sensor to aid GNSSpositioning, providing correction information a GNSS receiver to improveperformance of the GNSS receiver, performing positioning estimationusing a processor that is different from a GNSS receiver

In some implementations, a value (e.g., “urban canyon”) of a tilecategory sent to a mobile device can trigger the mobile device to submita second request for geographic feature data. The second request caninclude at least one of an identifier of a signal environment tile or anestimated position. The system can receive the second request from themobile device. In response, the system can identify a signal environmenttile based on the identifier or estimated position. The systemgeographic feature data in the identified signal environment tile to themobile device as a response to the second request

Exemplary Mobile Device Architecture

FIG. 11 is a block diagram illustrating an exemplary device architecture1100 of a mobile device implementing the features and operationsdescribed in reference to FIGS. 1-10C. A mobile device can includememory interface 1102, one or more data processors, image processorsand/or processors 1104 and peripherals interface 1106. Memory interface1102, one or more processors 1104 and/or peripherals interface 1106 canbe separate components or can be integrated in one or more integratedcircuits. Processors 1104 can include application processors, basebandprocessors and wireless processors. The various components in the mobiledevice, for example, can be coupled by one or more communication busesor signal lines.

Sensors, devices and subsystems can be coupled to peripherals interface1106 to facilitate multiple functionalities. For example, motion sensor1110, light sensor 1112 and proximity sensor 1114 can be coupled toperipherals interface 1106 to facilitate orientation, lighting andproximity functions of the mobile device. Location processor 1115 can beconnected to peripherals interface 1106 to provide geopositioning. Insome implementations, location processor 1115 can be program to performthe GNSS receiver 702. Electronic magnetometer 1116 (e.g., an integratedcircuit chip) can also be connected to peripherals interface 1106 toprovide data that can be used to determine the direction of magneticNorth. Thus, electronic magnetometer 1116 can be used as an electroniccompass. Motion sensor 1110 can include one or more accelerometersconfigured to determine change of speed and direction of movement of themobile device. Barometer 1117 can include one or more devices connectedto peripherals interface 1106 and configured to measure pressure ofatmosphere around the mobile device.

Camera subsystem 1120 and an optical sensor 1122, e.g., a chargedcoupled device (CCD) or a complementary metal-oxide semiconductor (CMOS)optical sensor, can be utilized to facilitate camera functions, such asrecording photographs and video clips.

Communication functions can be facilitated through one or more wirelesscommunication subsystems 1124, which can include radio frequencyreceivers and transmitters and/or optical (e.g., infrared) receivers andtransmitters. The specific design and implementation of thecommunication subsystem 1124 can depend on the communication network(s)over which a mobile device is intended to operate. For example, a mobiledevice can include communication subsystems 1124 designed to operateover a GSM network, a GPRS network, an EDGE network, a Wi-Fi™ or WiMax™network and a Bluetooth™ network. In particular, the wirelesscommunication subsystems 1124 can include hosting protocols such thatthe mobile device can be configured as a base station for other wirelessdevices.

Audio subsystem 1126 can be coupled to a speaker 1128 and a microphone1130 to facilitate voice-enabled functions, such as voice recognition,voice replication, digital recording and telephony functions. Audiosubsystem 1126 can be configured to receive voice commands from theuser.

I/O subsystem 1140 can include touch surface controller 1142 and/orother input controller(s) 1144. Touch surface controller 1142 can becoupled to a touch surface 1146 or pad. Touch surface 1146 and touchsurface controller 1142 can, for example, detect contact and movement orbreak thereof using any of a plurality of touch sensitivitytechnologies, including but not limited to capacitive, resistive,infrared and surface acoustic wave technologies, as well as otherproximity sensor arrays or other elements for determining one or morepoints of contact with touch surface 1146. Touch surface 1146 caninclude, for example, a touch screen.

Other input controller(s) 1144 can be coupled to other input/controldevices 1148, such as one or more buttons, rocker switches, thumb-wheel,infrared port, USB port and/or a pointer device such as a stylus. Theone or more buttons (not shown) can include an up/down button for volumecontrol of speaker 1128 and/or microphone 1130.

In one implementation, a pressing of the button for a first duration maydisengage a lock of the touch surface 1146; and a pressing of the buttonfor a second duration that is longer than the first duration may turnpower to the mobile device on or off. The user may be able to customizea functionality of one or more of the buttons. The touch surface 1146can, for example, also be used to implement virtual or soft buttonsand/or a keyboard.

In some implementations, the mobile device can present recorded audioand/or video files, such as MP3, AAC and MPEG files. In someimplementations, the mobile device can include the functionality of anMP3 player. Other input/output and control devices can also be used.

Memory interface 1102 can be coupled to memory 1150. Memory 1150 caninclude high-speed random access memory and/or non-volatile memory, suchas one or more magnetic disk storage devices, one or more opticalstorage devices and/or flash memory (e.g., NAND, NOR). Memory 1150 canstore operating system 1152, such as iOS, Darwin, RTXC, LINUX, UNIX, OSX, WINDOWS, or an embedded operating system such as VxWorks. Operatingsystem 1152 may include instructions for handling basic system servicesand for performing hardware dependent tasks. In some implementations,operating system 1152 can include a kernel (e.g., UNIX kernel).

Memory 1150 may also store communication instructions 1154 to facilitatecommunicating with one or more additional devices, one or more computersand/or one or more servers. Memory 1150 may include graphical userinterface instructions 1156 to facilitate graphic user interfaceprocessing; sensor processing instructions 1158 to facilitatesensor-related processing and functions; phone instructions 1160 tofacilitate phone-related processes and functions; electronic messaginginstructions 1162 to facilitate electronic-messaging related processesand functions; web browsing instructions 1164 to facilitate webbrowsing-related processes and functions; media processing instructions1166 to facilitate media processing-related processes and functions;GNSS/Location instructions 1168 to facilitate generic GNSS andlocation-related processes and instructions; camera instructions 1170 tofacilitate camera-related processes and functions; magnetometer data1172 and calibration instructions 1174 to facilitate magnetometercalibration. The memory 1150 may also store other software instructions(not shown), such as security instructions, web video instructions tofacilitate web video-related processes and functions and/or web shoppinginstructions to facilitate web shopping-related processes and functions.In some implementations, the media processing instructions 1166 aredivided into audio processing instructions and video processinginstructions to facilitate audio processing-related processes andfunctions and video processing-related processes and functions,respectively. An activation record and International Mobile EquipmentIdentity (IMEI) or similar hardware identifier can also be stored inmemory 1150. Memory 1150 can store position correction instructions 1176that, when executed by processor 1104, can cause processor 1104 toperform positioning correction operations, for example, the operationsdescribed above in various examples in reference to various figures.

Each of the above identified instructions and applications cancorrespond to a set of instructions for performing one or more functionsdescribed above. These instructions need not be implemented as separatesoftware programs, procedures, or modules. Memory 1150 can includeadditional instructions or fewer instructions. Furthermore, variousfunctions of the mobile device may be implemented in hardware and/or insoftware, including in one or more signal processing and/or applicationspecific integrated circuits.

FIG. 12 is a block diagram of an example network operating environment1200 for the mobile devices of FIGS. 1-10. Mobile devices 1202 a and1202 b can, for example, communicate over one or more wired and/orwireless networks 1210 in data communication. For example, a wirelessnetwork 1212, e.g., a cellular network, can communicate with a wide areanetwork (WAN) 1214, such as the Internet, by use of a gateway 1216.Likewise, an access device 1218, such as an 802.11g wireless accesspoint, can provide communication access to the wide area network 1214.Each of mobile devices 1202 a and 1202 b can be mobile device 102.

In some implementations, both voice and data communications can beestablished over wireless network 1212 and the access device 1218. Forexample, mobile device 1202 a can place and receive phone calls (e.g.,using voice over Internet Protocol (VoIP) protocols), send and receivee-mail messages (e.g., using Post Office Protocol 3 (POP3)), andretrieve electronic documents and/or streams, such as web pages,photographs, and videos, over wireless network 1212, gateway 1216, andwide area network 1214 (e.g., using Transmission ControlProtocol/Internet Protocol (TCP/IP) or User Datagram Protocol (UDP)).Likewise, in some implementations, the mobile device 1202 b can placeand receive phone calls, send and receive e-mail messages, and retrieveelectronic documents over the access device 1218 and the wide areanetwork 1214. In some implementations, mobile device 1202 a or 1202 bcan be physically connected to the access device 1218 using one or morecables and the access device 1218 can be a personal computer. In thisconfiguration, mobile device 1202 a or 1202 b can be referred to as a“tethered” device.

Mobile devices 1202 a and 1202 b can also establish communications byother means. For example, wireless device 1202 a can communicate withother wireless devices, e.g., other mobile devices, cell phones, etc.,over the wireless network 1212. Likewise, mobile devices 1202 a and 1202b can establish peer-to-peer communications 1220, e.g., a personal areanetwork, by use of one or more communication subsystems, such as theBluetooth™ communication devices. Other communication protocols andtopologies can also be implemented.

The mobile device 1202 a or 1202 b can, for example, communicate withone or more services 1230 and 1240 over the one or more wired and/orwireless networks. For example, one or more building model services 1230can provide signal environment tile data including tile categories andgeographic feature data including 3D building models to mobile devices1202 a and 1202 b from location server 502. Map service 1240 providevirtual maps for to mobile devices 1202 a and 1202 b for displayingestimated positions.

Mobile device 1202 a or 1202 b can also access other data and contentover the one or more wired and/or wireless networks. For example,content publishers, such as news sites, Really Simple Syndication (RSS)feeds, web sites, blogs, social networking sites, developer networks,etc., can be accessed by mobile device 1202 a or 1202 b. Such access canbe provided by invocation of a web browsing function or application(e.g., a browser) in response to a user touching, for example, a Webobject.

Example System Architecture

FIG. 13 is a block diagram of a system architecture for example locationserver 502. Other architectures are possible, including architectureswith more or fewer components. In some implementations, architecture1300 includes one or more processors 1302 (e.g., dual-core Intel® Xeon®Processors), one or more output devices 1304 (e.g., LCD), one or morenetwork interfaces 1306, one or more input devices 1308 (e.g., mouse,keyboard, touch-sensitive display) and one or more computer-readablemedia 1312 (e.g., RAM, ROM, SDRAM, hard disk, optical disk, flashmemory, etc.). These components can exchange communications and dataover one or more communication channels 1310 (e.g., buses), which canutilize various hardware and software for facilitating the transfer ofdata and control signals between components.

The term “computer-readable medium” refers to a medium that participatesin providing instructions to processor 1302 for execution, includingwithout limitation, non-volatile media (e.g., optical or magneticdisks), volatile media (e.g., memory) and transmission media.Transmission media includes, without limitation, coaxial cables, copperwire and fiber optics.

Computer-readable medium 1312 can further include operating system 1314(e.g., a Linux® operating system), network communication module 1316,empirical data manager 1320, geographic information manager 1330 andgeographic feature data manager 1340. Operating system 1314 can bemulti-user, multiprocessing, multitasking, multithreading, real time,etc. Operating system 1314 performs basic tasks, including but notlimited to: recognizing input from and providing output to networkinterfaces 1306 and/or devices 1308; keeping track and managing filesand directories on computer-readable media 1312 (e.g., memory or astorage device); controlling peripheral devices; and managing traffic onthe one or more communication channels 1310. Network communicationsmodule 1316 includes various components for establishing and maintainingnetwork connections (e.g., software for implementing communicationprotocols, such as TCP/IP, HTTP, etc.).

Empirical data manager 1320 can include computer instructions that, whenexecuted, cause processor 1302 to receive empirical data including datafrom experiments of GNSS signal interference caused by variousgeographic features in various terrains. The data can be tagged with aterrain types, which can correspond to tile category types. Geographicinformation manager 1330 can include computer instructions that, whenexecuted, cause processor 1302 to receive geographic information fromvarious sources and generate one or more 3D building models. Geographicfeature data manager 1340 can include computer instructions that, whenexecuted, cause processor 1302 to perform operations of generatingsignal information tiles using geographic information, assigning tilecategories to the generated tiles, and provide geographic data and othertile information to a mobile device upon request.

Architecture 1300 can be implemented in a parallel processing orpeer-to-peer infrastructure or on a single device with one or moreprocessors. Software can include multiple software components or can bea single body of code.

The described features can be implemented advantageously in one or morecomputer programs that are executable on a programmable system includingat least one programmable processor coupled to receive data andinstructions from, and to transmit data and instructions to, a datastorage system, at least one input device, and at least one outputdevice. A computer program is a set of instructions that can be used,directly or indirectly, in a computer to perform a certain activity orbring about a certain result. A computer program can be written in anyform of programming language (e.g., Objective-C, Java), includingcompiled or interpreted languages, and it can be deployed in any form,including as a stand-alone program or as a module, component,subroutine, a browser-based web application, or other unit suitable foruse in a computing environment.

Suitable processors for the execution of a program of instructionsinclude, by way of example, both general and special purposemicroprocessors, and the sole processor or one of multiple processors orcores, of any kind of computer. Generally, a processor will receiveinstructions and data from a read-only memory or a random access memoryor both. The essential elements of a computer are a processor forexecuting instructions and one or more memories for storing instructionsand data. Generally, a computer will also include, or be operativelycoupled to communicate with, one or more mass storage devices forstoring data files; such devices include magnetic disks, such asinternal hard disks and removable disks; magneto-optical disks; andoptical disks. Storage devices suitable for tangibly embodying computerprogram instructions and data include all forms of non-volatile memory,including by way of example semiconductor memory devices, such as EPROM,EEPROM, and flash memory devices; magnetic disks such as internal harddisks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROMdisks. The processor and the memory can be supplemented by, orincorporated in, ASICs (application-specific integrated circuits).

To provide for interaction with a user, the features can be implementedon a computer having a display device such as a CRT (cathode ray tube)or LCD (liquid crystal display) monitor or a retina display device fordisplaying information to the user. The computer can have a touchsurface input device (e.g., a touch screen) or a keyboard and a pointingdevice such as a mouse or a trackball by which the user can provideinput to the computer. The computer can have a voice input device forreceiving voice commands from the user.

The features can be implemented in a computer system that includes aback-end component, such as a data server, or that includes a middlewarecomponent, such as an application server or an Internet server, or thatincludes a front-end component, such as a client computer having agraphical user interface or an Internet browser, or any combination ofthem. The components of the system can be connected by any form ormedium of digital data communication such as a communication network.Examples of communication networks include, e.g., a LAN, a WAN, and thecomputers and networks forming the Internet.

The computing system can include clients and servers. A client andserver are generally remote from each other and typically interactthrough a communication network. The relationship of client and serverarises by virtue of computer programs running on the respectivecomputers and having a client-server relationship to each other. In someembodiments, a server transmits data (e.g., an HTML page) to a clientdevice (e.g., for purposes of displaying data to and receiving userinput from a user interacting with the client device). Data generated atthe client device (e.g., a result of the user interaction) can bereceived from the client device at the server.

A system of one or more computers can be configured to performparticular actions by virtue of having software, firmware, hardware, ora combination of them installed on the system that in operation causesor cause the system to perform the actions. One or more computerprograms can be configured to perform particular actions by virtue ofincluding instructions that, when executed by data processing apparatus,cause the apparatus to perform the actions.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of anyinventions or of what may be claimed, but rather as descriptions offeatures specific to particular embodiments of particular inventions.Certain features that are described in this specification in the contextof separate embodiments can also be implemented in combination in asingle embodiment. Conversely, various features that are described inthe context of a single embodiment can also be implemented in multipleembodiments separately or in any suitable subcombination. Moreover,although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asubcombination or variation of a subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the embodiments described above should not be understoodas requiring such separation in all embodiments, and it should beunderstood that the described program components and systems cangenerally be integrated together in a single software product orpackaged into multiple software products.

Thus, particular embodiments of the subject matter have been described.Other embodiments are within the scope of the following claims. In somecases, the actions recited in the claims can be performed in a differentorder and still achieve desirable results. In addition, the processesdepicted in the accompanying figures do not necessarily require theparticular order shown, or sequential order, to achieve desirableresults. In certain implementations, multitasking and parallelprocessing may be advantageous.

A number of implementations of the invention have been described.Nevertheless, it will be understood that various modifications can bemade without departing from the spirit and scope of the invention.

What is claimed is:
 1. A method comprising: receiving, by a processor ofa mobile device and from a global navigation satellite system (GNSS)receiver, an estimated position of the mobile device, the estimatedposition including estimated geographic coordinates and being associatedwith an uncertainty value; receiving geographic feature data, thegeographic feature data including locations and heights of geographicfeatures that are located sufficiently close to the estimated positionto interfere with signals received by the GNSS receiver; determining,based on at least one of the locations of the geographic features, acount of the geographic features, or the heights of the geographicfeatures, a lower bound of uncertainty of the estimated position that isachievable by the GNSS receiver when the GNSS receiver is located amongthe geographic features; determining, based on the lower bound ofuncertainty, a new estimated position of the mobile device; anddesignating a representation of the lower bound of uncertainty as arepresentation of uncertainty of the new estimated position of themobile device.
 2. The method of claim 1, wherein receiving geographicfeature data comprises: determining a signal environment tile based onthe estimated position, the signal environment tile representinggeographic features located in a geographic region that may interferewith GNSS signal reception, the geographic region being an areasurrounding the estimated position; determining, based on a tilecategory of the signal environment tile, that the geographic featuredata of the signal environment tile can improve position estimate;submitting the estimated position or an identifier of the signalenvironment tile to a signal environment tile database, the signalenvironment tile database storing three-dimensional models on geographicfeatures, the three-dimensional models being organized as a plurality ofsignal environment tiles; and receiving the geographic feature datacorresponding to the signal environment tile.
 3. The method of claim 2,wherein determining the lower bound of uncertainty of the estimatedposition comprises determining the lower bound based on a predeterminedfactor and a width of an average road located in the geographic regionenclosing the estimated position.
 4. The method of claim 1, whereindetermining the lower bound of uncertainty comprises: determiningsatellites that visible by the GNSS receiver at the estimated position;determining a weight dilution of precision based on the visiblesatellites; and determining the lower bound of uncertainty based on theweight dilution of precision.
 5. The method of claim 1, whereindetermining the lower bound of uncertainty comprises: determiningwhether the count of the geographic features located sufficiently closeto the GNSS receiver to interfere reception of the GNSS signalssatisfies a feature count threshold; determining whether an average ofheights of the geographic features located sufficiently close to theGNSS receiver to interfere reception of the GNSS signals satisfies afeature height threshold; and determining the lower bound of uncertaintywhen both the feature count threshold and feature height are satisfied.6. The method of claim 1, comprising: determining that the estimatedgeographic coordinates indicate a position inside of a geographicfeature; and designating a set of geographic coordinates outside of thegeographic feature as new estimated geographic coordinates of theestimated position.
 7. The method of claim 1, comprising displaying arepresentation of the estimated position on a map displayed on themobile device, wherein a size of an area of the estimated positionrepresents the lower bound of uncertainty.
 8. A mobile devicecomprising: a global navigation satellite system (GNSS) receiverincluding an interface to adjust coherent integration interval ofprocessing GNSS signals; one or more processors; and a non-transitorycomputer-readable medium storing instructions that, when executed by theone or more processors, cause the one or more processors to performoperations comprising: receiving, by a processor of the mobile deviceand from the global navigation satellite system (GNSS) receiver, anestimated position of the mobile device, the estimated positionincluding estimated geographic coordinates and being associated with anuncertainty value; receiving geographic feature data, the geographicfeature data including locations and heights of geographic features thatare located sufficiently close to the estimated position to interferewith signals received by the GNSS receiver; determining, based on atleast one of the locations of the geographic features, a count of thegeographic features, or the heights of the geographic features, a lowerbound of uncertainty of the estimated position that is achievable by theGNSS receiver when the GNSS receiver is located among the geographicfeatures; determining, based on the lower bound of uncertainty, a newestimated position of the mobile device; and designating arepresentation of the lower bound of uncertainty as a representation ofuncertainty of the new estimated position of the mobile device.
 9. Themobile device of claim 8, wherein receiving geographic feature datacomprises: determining a signal environment tile based on the estimatedposition, the signal environment tile representing geographic featureslocated in a geographic region that may interfere with GNSS signalreception, the geographic region being an area surrounding the estimatedposition; determining, based on a tile category of the signalenvironment tile, that the geographic feature data of the signalenvironment tile can improve position estimate; submitting the estimatedposition or an identifier of the signal environment tile to a signalenvironment tile database, the signal environment tile database storingthree-dimensional models on geographic features, the three-dimensionalmodels being organized as a plurality of signal environment tiles; andreceiving the geographic feature data corresponding to the signalenvironment tile.
 10. The mobile device of claim 9, wherein determiningthe lower bound of uncertainty of the estimated position comprisesdetermining the lower bound based on a predetermined factor and a widthof an average road located in the geographic region enclosing theestimated position.
 11. The mobile device of claim 8, whereindetermining the lower bound of uncertainty comprises: determiningsatellites that visible by the GNSS receiver at the estimated position;determining a weight dilution of precision based on the visiblesatellites; and determining the lower bound of uncertainty based on theweight dilution of precision.
 12. The mobile device of claim 8, whereindetermining the lower bound of uncertainty comprises: determiningwhether the count of the geographic features located sufficiently closeto the GNSS receiver to interfere reception of the GNSS signalssatisfies a feature count threshold; determining whether an average ofheights of the geographic features located sufficiently close to theGNSS receiver to interfere reception of the GNSS signals satisfies afeature height threshold; and determining the lower bound of uncertaintywhen both the feature count threshold and feature height are satisfied.13. A non-transitory computer-readable medium storing instructions that,when executed by one or more processors, cause the one or moreprocessors to perform operations comprising: receiving geographicinformation on geographic features in a geographic area, the geographicfeatures including structures that are estimated to interfere withreception of wireless signals at a location in the geographic area;grouping the geographic information into signal environment tiles ofgeographic feature data, each signal environment tile comprising ageometric shape occupying a respective geographic region in thegeographic area; assigning a respective tile category to each signalenvironment tile, each tile category indicating a respectiverelationship between an uncertainty in global navigation satellitesystem (GNSS) positioning and a position of a satellite of the GNSS, therelationship being constrained by geographic features located in thecorresponding geometric region; and upon receiving a request thatindicates an estimated position from a mobile device, providing a tilecategory assigned to a signal environment tile of a geometric regionenclosing the estimated position as a response to the request.
 14. Thenon-transitory computer-readable medium of claim 13, wherein thegeographic information includes one or more of: a wireless access pointdensity in the geographic area, a digital surface model of thegeographic area, a three-dimensional building model of the geographicarea, a geographic survey of the geographic area, or a satellite imageof the geographic area.
 15. The non-transitory computer-readable mediumof claim 13, wherein each geometric shape is a polygon represented bylatitude and longitude coordinates.
 16. The non-transitorycomputer-readable medium of claim 13, wherein each tile categorycorresponds to a specified range of density and heights of geographicfeatures.
 17. The non-transitory computer-readable medium of claim 16,wherein: a first signal environment tile has a first tile category, asecond signal environment tile has a second category, the first tilecategory and the second tile category indicating that density andheights of geographic features in a geographic region of the firstsignal environment tile are less than density and heights of geographicfeatures in geographic region the second signal environment tile, and ata same satellite elevation, the uncertainty in GNSS positioning is lowerfor the first tile category than for the second tile category.
 18. Thenon-transitory computer-readable medium of claim 13, wherein at leastone tile category is associated with a value for triggering a downloadof a three-dimensional building model of geographic features inproximity to the estimated position by the mobile device.
 19. Thenon-transitory computer-readable medium of claim 13, wherein at leastone tile category is associated with a value for triggering the mobiledevice to determine a position by performing one or more of: enabling aninertial sensor to aid GNSS positioning; providing correctioninformation a GNSS receiver to improve performance of the GNSS receiver;or performing positioning estimation using a processor that is differentfrom a GNSS receiver.
 20. The non-transitory computer-readable medium ofclaim 13, the operations comprising: receiving a second request from themobile device, the second request including at least one of anidentifier of a signal environment tile or an estimated position, thesecond request indicating that the mobile device requests geographicfeature data; in response to the second request, identifying a signalenvironment tile based on the identifier or estimated position; andproviding geographic feature data in the identified signal environmenttile to the mobile device as a response to the second request.